[46086] in Cypherpunks
easy avoidance of PGP signature forgeries and reuse
daemon@ATHENA.MIT.EDU (attila)
Fri Dec 29 14:11:55 1995
Date: Fri, 29 Dec 1995 18:07:17 +0000 (GMT)
From: attila <attila@primenet.com>
To: "Dr. Dimitri Vulis" <dlv@bwalk.dm.com>
Cc: cypherpunks@toad.com
In-Reply-To: <oTTsgD7w165w@bwalk.dm.com>
START <attila>
I never paid much attention to the problem other than to avoid
it by forcing it --i.e. list the destination and the send inside the
signature block, thus:
----------------- BEGIN PGP SIGNED TEXT
To: john doe <john@box.com>
Newsgroups: sci.crypt
From: jane roe <jane@topsey.turvey.com>
Subject: that's all folks!
John, don't darken my door during the Christmas holidays.
Nevermore.
jane
---------------- BEGIN PGP SIGNATURE
ERTYUIKJBNM,./34567JM,./
---------------- END PGP SIGNATURE
with e-mail, e-letters, direct faxes, etc. it is to easy to
ignore the courtesy header. From a standpoint of security, you have
blown away each of the attacks outline in your article in so much as
the signature will not compute if the courtesy block is omitted.
personally, I do not think PGP 3 should attempt to solve the
problem. Most of the headers involved are applied _after_ the message
leaves the mail program; and, PGP interfaces are virtually the same
as invoking an alternate editor, which gets you nothing.
END <attila>
--
--------------------------------------------------------------------
#!/bin/perl -s-- -export-a-crypto-system-sig -RSA-3-lines-PERL
$m=unpack(H.$w,$m."\0"x$w),$_=`echo "16do$w 2+4Oi0$d*-^1[d2%Sa
2/d0<X+d*La1=z\U$n%0]SX$k"[$m*]\EszlXx++p|dc`,s/^.|\W//g,print
pack('H*',$_)while read(STDIN,$m,($w=2*$d-1+length$n&~1)/2)
